Biosorption system

ABSTRACT

The invention relates to a system, process and apparatus for separating biosorbent and sorbate. Biomass enclosed within a membrane system is coupled to an electrode, which is capable of being placed in contact with the sorbate containing material in the presence of a counter electrode. An electric field may be discharged across the electrodes and ionic species will migrate into the membrane enclosed system. The migrated species within the membrane can be taken up and processed by the biosorbtive processes of the biomass. The system may be used to remove dye stuffs, metal, heavy metals, radionuclides and other pollutants from natural and artificial sources.

This application is the U.S. national phase application of PCTInternational Application No. PCT/GB97/03441 filed Dec. 15, 1997.

This invention relates to biosorption processes for removal and recoveryof heavy metals, radionuclides, pollutants and other materials from theenvironment.

The existence of heavy metals and radionuclides and pollutants such asdye stuffs in the environment represent a long-term environmental hazard(Gadd and White [1993] Trends in Biotechnol., 11, 353). In many cases,when these materials are introduced into the environment they are takenup by biological systems including plant and microbial materials. It hasbeen proposed that this phenomenon, known as biosorption, might beexploited in biotechnological processes relating to metalremoval/recovery from mining wastes, domestic and industrial wastes andremoval of radionuclide contaminants present in waste waters from thenuclear industry (McHale & McHale, [1994] Biotechnol. Advances, 12,647).

Although biosorption results in the uptake of metals and radionuclidesby microorganisms, no single mechanism responsible for uptake has beenidentified. The term “adsorption” suggests binding of a material to thesurface of an adsorbent. The term “absorption” implies penetration ofthe sorbate through the surface to an inner matrix. Since the uptake ofmetals/radionuclides and other agents by microbes appears to involveboth types of process, the term “biosorption” is most commonly appliedto describe the phenomenon.

In any previously proposed bioremediation systems concerned withexploiting biosorptive processes, one of the major problems encounteredhas been the efficient separation of the biosorbent material from therelevant waste water stream, particularly if large volumes are to beprocessed. In many cases workers in the field have suggested the use ofimmobilization systems in order to facilitate re-use of the biosorbentmaterial. It has also been proposed that this would also facilitateefficient separation from the relevant waste-water stream and aid in theregeneration of the biosorbent (McHale & McHale [1994] (BiotechnolAdvances), 12, 647).

In addition to the above complications associated with the exploitationof biosorptive processes, solutions of metals/radionuclides and otherpollutants in waste-water streams tend to be very dilute. Sincebiosorptive processes, particularly using non-living biomass are in manycases equilibrium events, the inventors have found that uptake of therelevant sorbate is usually enhanced by positively disturbing thoseequilibria. They postulate that increasing the concentration of thesorbate in the vicinity of the biosorbent may tend to increase thedegree of uptake exhibited by any form of biomass.

Distribution of ions across a semipermeable membrane is also anequilibrium event. However, removal of free or soluble ions fromsolution within a membrane enclosed compartment tends to unbalance thatequilibrium and the net flow of ions into the membrane enclosed space.The inventors suggest that placing biosorbent material inside amembrane-enclosed compartment and exposing this to an external solutionof ions would result in a net flow of those ions into the enclosedspace. In effect this would achieve ion removal from the externalsolution by a mechanism known as non-equilibrium dialysis. It has theadded advantage of ensuring biosorbent and sorbate separation before,during and after the ion removal/recovery process.

Although this offers many advantages over conventional biosorptionprocesses, this type of system would be highly dependant on the rate ofdiffusion into the inner compartment. It has previously been shownhowever that it is possible to attract ions into membrane-enclosedcompartments using an electric field and this is referred to aelectrodialysis (Bobrinskaya et al., [1995] Russian J. Applied Chem. 68,1205; Ishimaru [1994] Desalination, 98, 485.). It has been suggestedthat this may be exploited in processes such as desalination of wateralthough it is worth noting that removal of the applied electric fieldin conventional electrodialysis modalities, results in leakage of therelevant ions from the membrane-enclosed space.

It is one object of the present invention to provide a system to removeand/or recover heavy metals/metals/ionic species/radionuclides and/orpollutants in general from the environment.

According to the present invention there is provided a system forseparating biosorbent and sorbate, the system comprising biomassenclosed within a membrane system coupled to an electrode capable ofbeing placed in contact with sorbate containing material in the presenceof a counter electrode such that an electric field may be dischargedacross the electrodes and ionic species will migrate into the membraneenclosed system.

Accordingly in one aspect the invention provides a biosorption processcomprising exposing sorbate containing material to biomass enclosedwithin a membrane system and generating an electric field across themembrane thereby causing sorbate to migrate to the biomass.

In another aspect the invention provides biosorption apparatuscomprising biomass enclosed within a membrane system coupled to orcapable of being coupled to an electrode.

In another aspect the invention relates to the use of immobilisedbiomass in a system, apparatus or process as described herein.

The biomass material may be living or non-living, modified ornon-modified, free or immobilised or any combination of these forms.

In a particular embodiment the biomass is distillery biomass.

In the system the migrated species within the membrane can be taken upand processed by the biosorptive processes of the biomass.

The electric field in the system may be generated in a conventionalmanner and/or from renewable energy sources including solar, wind andwave energy forms.

Suitably the system may be used to remove metals/heavymetals/radionuclides and/or other pollutants from natural and artificialsources and/or combinations thereof.

In one embodiment the invention provides an apparatus comprisingmodified non-living biomass enclosed within a membrane system coupled toa platinum electrode.

Alternatively the biomass may be non-living.

The electrode may be of any other electrode material.

The apparatus may be placed in contact with the sorbate-containingmaterial in the present of a counter electrode. An electric field willbe discharged across the electrodes and the ionic species will migrateinto the membrane enclosed system. The migrated species within themembrane enclosed space will then be taken up by the biosorptiveprocesses exhibited by the biomass.

The living or non-living biomass may be modified.

The living or non-living biomass may be immobilised.

In the embodiment described above the electric filed may be generated inthe conventional manner and/or from renewable energy resourcesincluding, although not exclusively, solar, wind and wave energy forms.

In another embodiment the invention provides a device (or derivativethereof) based on the use of electrodiffusion-assisted biosorption andcapable of removing metals/heavy metals/radionuclides/and/or otherpollutants from natural and artificial sources and/or combinationsthereof) for the purposes of bioremediation and/or substance recovery.

The device (or derivative thereof) based on the use ofelectrodiffusion-assisted biosorption may be capable of concentratingagents for analytical purposes.

In a third embodiment the invention provides a system capable ofgeneration of ionic species and subsequent sequestration of these by thesystems described herein.

The embodiments of the invention may be operated in batch, fed-batchand/or continuous modes including combinations thereof.

The embodiments of the invention may be operated in conjunction withother processes.

The invention will comprise any of the above systems and/or combinationsof the above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the following examplesand the accompanying drawings wherein:

FIG. 1 illustrates the sequestration of uranium at relatively highconcentrations using the electrodiffusion-assisted biosorptionsystem/process.

FIG. 2 illustrates removal of uranium (at relatively low concentrations)for solution using the electrodiffusion-assisted biosorptionsystem/process.

FIG. 3 illustrates removal of lead from solution using theelectrodiffusion-assisted biosorption system/process.

FIG. 4 illustrates biosorption of Remazol red, golden yellow and black Bdyes by 1 g/L distillery biomass.

EXAMPLE 1 Removal of relatively high concentrations of uranium fromsolution using electrodiffusion-assisted biosorption:

In these studies waste biomass was obtained from industrial processesconcerned with alcohol production for the beverage industry. The biomasswas washed by centrifugation at 10,000 xg for 20 min. and subsequentlyfreeze dried. In the experiments described here 1 g (dry weight) biomasswas resuspended in 10 ml of distilled water. This was then placed indialysis tubing (Visking tubing) which was closed at one end. Themembrane-enclosed system was fixed in place in a beaker containing 500ml of 1 mM uranyl acetate. A platinum wire electrode (negative in thiscase) was placed inside the open end of the dialysis tubing which wasvented to the air. The other electrode was placed in the externalsolution. The electrodes were connected to a power pack which was set todeliver a constant voltage of 20 V (it should be noted that the proposeddevices and/or systems described herein will not be restricted withrespect to delivered electric parameters or electric field strengths).Samples from the external solution were harvested at various times andthe concentration of uranium was determined using the method describedby Savvin ([1961], Talanta, 8, 673). In these experiments controlsystems consisted of either biomass inside the dialysis membrane withoutan applied electric field and using the dialysis membrane withoutbiomass but with an applied electric field. The results obtained fromthese experiments are shown in FIG. 1. In the control consisting of thebiomass and no applied electric field (▪) the external concentration ofuranium decreased from 195 mg/L to 119 mg/L over a 25 hour period (FIG.1). In the control involving the use of the electric field in theabsence of biomass (▾) the external uranium concentration decreased from190 mg/L to 79 mg/L over a 21 hour period. In the test system consistingof the biomass and electrodiffusion-assisted transfer of uranium intothe enclosed compartment (▴), the external uranium concentrationdecreased from 195 mg/L to 33 mg/L over a 23 hour period. Thisdemonstrated that 162 mg of uranium had concentrated within the 10 mlvolume inside the dialysis tubing. It is also worth noting that at eachtime point the external concentration of uranium in the electrodiffusionsystem containing the biomass was lower than that in the system withoutthe biomass, hence our use of the term “electrodiffusion-assistedbiosorption”.

EXAMPLE 2 Removal of relatively ow concentrations of uranium fromsolution using the electrodiffusion-assisted biosorption system:

The experimental configuration described for Example 1 was similar inthese experiments except that the external concentration of uranium wasadjusted from 1 mM to 0.074 mM. In addition 0.5 g of biomass wassuspended in 5 ml of distilled water and this was placed inside thedialysis tubing. This was then inserted into a beaker containing 250 mlof the uranium solution. In this case the control consisted of biomassbut in the absence of applied electric field. The results are shown inFIG. 2. In the control system (▴) the concentration of uranium decreasedfrom 17.4 mg/L to 2.86 mg/L within 24 hours and to 1.42 mg/L within 48hours. In the test system (▪) however the concentration of uraniumdecreased from 17.6 mg/L to 0.5 mg/L in 24 hours and to 0.3 mg/L within48 hours. It should be noted that the figure of 0.3 mg/L for theconcentration of uranium is outside the lower confidence limits of theassay used to detect uranium.

EXAMPLE 3 Removal of lead from solution using theelectrodiffusion-assisted biosorption system:

In this part of the study a similar configuration to that used inExample 2 above was used except that the uranium solution was replacedwith lead nitrate at a concentration of 230 mg/L. In addition theconcentration of lead was determined using atomic absorptionspectrophotometry. The control consisted of biomass within themembrane-enclosed compartment and no electric field was applied. Theresults are shown in FIG. 3. In the control system (▪) the externalconcentration of lead decreased to a concentration of 216.7 mg/L after41 hours. In the test system (▴) the external concentration of leaddecreased to 18.7 mg/L indicating a 91.9% overall decrease in externalconcentrations.

EXAMPLE 4 Biosorption of textile dyes by distillery-derived biomass:

The objective of this part of the study was to demonstrate that thedistillery-derived biomass was capable of textile dye biosorption. Infulfilling this objective it was decided to employ commonly used textiledyes including Remazol red, golden yellow and Remazol black B. Solutionsof dye were prepared in distilled water and used as the sorbate. Theconcentrations of the Remazol red, Remazol golden yellow and the Remazolblack B were measured spectrophotometrically at 520, 410 and 600 nm,respectively. Biomass was placed in contact with the dye solution in 10ml contact reactions and those reactions were allowed to continue for aperiod of 12 hours. The biomass was then removed (by eithercentrifugation or membrane filtration [0.2 μm filtration units]) and theresidual concentration of dye (Ce mg/L) remaining in solution wasdetermined using a spectrophotometer. From those values the amount ofdye associated with the biomass q (mg/g dry weight biomass) wasdetermined and the data were used to construct biosorption isotherms.The results are shown in FIG. 4 which is a graph of q(mg/g) vs Ce(mg/L).The error bars represent S.E.M, n=6. This experiment demonstrates thatthe biomass is capable of binding significant quantities of dye. Fromthe data presented maximum biosorption capacities (q_(max) mg/g dryweight biomass) of 97, 107 and 62 mg/g were obtained for the Remazolred, Remazol golden yellow and Remazol black B, respectively.

EXAMPLE 5 Electrodiffusion assisted treatment of a textile dyecontaining effluent from William Clark & Sons Limited, a local textileprocessing plant: in Upperlands, Maghera, Co Londonderry.

One objective in this part of the study was to determine whether or notthe electrodiffusion assisted system might provide a novel andalternative means of treating and decolorising textile dye containingeffluent. In order to do this, it was decided to obtain a sample ofeffluent from a local textile processing plant, William Clark & SonsLimited, Upperlands, Maghera, Co Londonderry. Raw effluent was obtainedfrom a holding tank outlet at the plant. It had a murky blue greenappearance and contained a significant quantity of particulate material.This effluent was placed in the membrane-excluded space of theelectrodiffusion apparatus as described in Example 1 for themetal-bearing solutions. The normal electrode configuration involvedplacing the negative electrode in the membrane-enclosed space togetherwith the biomass. The positive electrode was placed in the effluentwhich was in the membrane-excluded space. The system was operated underthe same conditions described in Example 1 for a period of 12-24 hours.Results from a typical run are summarized in Table 1 . Parameters suchas suspended solids, the degree of decolorisation and removal of CODwere measured before and after treatment.

TABLE 1 Treatment of textile processing effluent using theelectrodiffusion-assited biosorption system Parameter measured BeforeAfter Suspended Solids 50-55   0-0.6 (mg/L) Decolorisation (%) 0 96-98Control 1* 0 33.9 Control 2* 0 34.6 COD (mg/L) 171 89 Control 1 for thedecolorisation experiments consisted of the system using only theelectrodes and excluding the biomass from the system whereas Control 2consisted of the biomass without the application of an electric field.

Suspended solid content was measured using dry weight analysis incombination with filtration though Whatman grade I filter paper. In theuntreated material the suspended solids were determined to be in theregion of 50-55 mg/L and this was reduced to 0.6 mg/L within a 12 hourperiod. In this case it appeared the evolution of gas from the positiveelectrode in the membrane-excluded space resulted in floatation ofparticulate material and this could be recovered by skimming from thetop of the treated solution. This also resulted in a significant degreeof decolorisation. In studying decolorisation it was found that theeffluents had a λ_(max) at 600 nm and therefore spectrophotometry couldbe used to examine this parameter. It was found that the system wascapable of removing 96-98% of the colour from the effluent and it shouldbe stated that the liquid in the membrane-excluded compartment wascolourless to the naked eye. In measuring the chemical oxygen demand(COD) of the treated and untreated effluent a commercial kit was used(Hach Europe Ltd., Belgium). It was found that almost 50% of the OD ofthe untreated effluents could be removed using the system. The resultsdemonstrate that the electrodiffusion system is capable of veryeffective treatment of textile processing effluents, particularly withrespect to decolorisation.

In summary, the examples described herein demonstrate the ability of theinvention to significantly reduce concentrations of a variety ofpollutants and other materials in the environment.

The invention is not limited to the embodiments described above whichmay clearly be modified and/or varied without departing from the scopeof the invention.

What is claimed is:
 1. A system for separating biosorbent and sorbate:the system comprising non-living biomass enclosed within a membranesystem coupled to an electrode capable of being placed in contact withsorbate containing material in the presence of a counter electrode suchthat an electric field may be discharged across the electrodes and ionicspecies will migrate into the membrane enclosed system.
 2. A system asclaimed in claim 1 wherein the non-living biomass material is modifiedor non-modified, immobilized or non-immobilised or any combination ofthese forms.
 3. A system as claimed in claim 1 or claim 2, wherein theelectric field in the system is generated from conventional energysources and/or from renewable sources including solar, wind and waveenergy forms.
 4. A system for separating biosorbent and sorbate asclaimed in claim 1 or 4, wherein the system is operated in batch,batch-fed and/or continuous mode including combinations thereof. 5.Immobilised non-living biomass for use in biosorption in a system asclaimed in claim
 1. 6. A biosorption process comprising the steps ofexposing sorbate containing material to non-living biomass enclosedwithin a membrane and generating an electric field in the sorbatecontaining material in the vicinity of the membrane thereby causingsorbate to migrate to the biomass.
 7. A process as claimed in claim 6wherein the biomass material is non-living, modified or non-modified,immobilised or non-immobilised, or any combination of these forms.
 8. Aprocess as claimed in claim 6 or 7 wherein the electric field in thesystem is generated from conventional energy sources and/or fromrenewable sources including solar, wind and wave energy forms.
 9. Aprocess as claimed in claim 6 wherein the non-living biomass isimmobilised.
 10. A biosorption apparatus comprising non-living biomassenclosed within a membrane coupled to an electrode.
 11. An apparatus asclaimed in claim 10 wherein the biomass material is non-living, modifiedor non-modified, immobilised or non-immobilised or any combination ofthese forms.
 12. A process for separating biosorbents and sorbate toallow the removal of metals, heavy metals, radionuclides and/or otherpollutants from natural and artificial sources and/or combinationsthereof, comprising the steps of enclosing a non-living biomass within amembrane, coupling this to an electrode, placing the electrode incontact with said sources in the presence of a counter electrode, anddischarging an electrical field across the electrodes, this effectingthe migration of the ionic species into the membrane enclosed system.